Damp line along middle of interior wall

[tvrulesme]

I've been slowly renovating an old 1800s listed building which was suffering from a lot of damp. I've managed to combat a lot of the damp in the house by installing French drains, fixing gutters, reverting to Lime plaster but there's one room which is completely throwing me and not sure how to move forward.

 

There is a damp line running along the centre of the bedroom wall which is an internal wall running at right angles to the exterior wall.

 

 

Floor plan of the house showing the damp wall

 

And a picture of the exterior wall with the position of the internal wall

 

 

It's not rising damp because it's in the middle of the wall and exterior ground levels are low. Gutters have been checked. Loft area above is dry with no leaks. Weather seems to make no difference. It's there when it's sunny and dry outside as well as when raining. 

 

Any ideas what investigation I should do next?

[joe90]

  On 05/12/2024 at 17:18, tvrulesme said:

It's not rising damp because it's in the middle of the wall

Expand  

Very often riding damp was “cured” by waterproof render from ground to 1 m high. Has this been applied in the past which might explain why “damp” shows above this line. Alternatively is it damp or stain?

[tvrulesme]

  On 05/12/2024 at 17:54, joe90 said:

Very often riding damp was “cured” by waterproof render from ground to 1 m high. Has this been applied in the past which might explain why “damp” shows above this line. Alternatively is it damp or stain?

Expand  

Thanks a lot @joe90. I hadn't thought of that. Do you mean inside or exterior? Outside is just painted brick. It's possible that some damp proffing happened inside. I'm not sure.

 

It's damp. If I stick a heater under it it dries out but comes back 

[joe90]

  On 05/12/2024 at 18:02, tvrulesme said:

It's damp. If I stick a heater under it it dries out but comes back 

Expand  

 

  On 05/12/2024 at 18:02, tvrulesme said:

Do you mean inside or exterior?

Expand  

But the wall is interior 🤷‍♂️ so both sides are internal?. With some damp proofing plaster was removed up to approx 1m and replaced with waterproof render. You don’t mention the other side of this internal wall..

[Mr Punter]

Is the damp evident on the dining room side?

[tvrulesme]

  On 05/12/2024 at 18:11, joe90 said:

 

But the wall is interior 🤷‍♂️ so both sides are internal?. With some damp proofing plaster was removed up to approx 1m and replaced with waterproof render. You don’t mention the other side of this internal wall..

Expand  

Ha yes, sorry I meant the wall at right angles to this one, the exterior wall. 

[tvrulesme]

  On 05/12/2024 at 18:11, Mr Punter said:

Is the damp evident on the dining room side?

Expand  

A tiny tiny bit. It's not damp but a little bit of paint has come away at the same height. 

[Mr Punter]

Could it be condensation?  If the room is occupied it could be generating a fair bit of moisture.  Would a dehumidifier help?

[joe90]

I think the wall has previously been “cured” as I said above with waterproof render (but shows it’s not!!!,) it’s a shame it’s all decorated as any work will cause mess. Unless you want to hack plaster off you won’t know. I would look into either an Injected damp course or cut a physical one in. It would mean removing the skirting board but save lots of messy other work 

[tvrulesme]

  On 05/12/2024 at 18:21, joe90 said:

I think the wall has previously been “cured” as I said above with waterproof render (but shows it’s not!!!,) it’s a shame it’s all decorated as any work will cause mess. Unless you want to hack plaster off you won’t know. I would look into either an Injected damp course or cut a physical one in. It would mean removing the skirting board but save lots of messy other work 

Expand  

It was hastily decorated. I'd be happy to hack stuff off to get to the bottom of it. It's a holiday home / mid life crisis renovation project. 

[tvrulesme]

  On 05/12/2024 at 18:20, Mr Punter said:

Could it be condensation?  If the room is occupied it could be generating a fair bit of moisture.  Would a dehumidifier help?

Expand  

It's not occupied all the time, a few days a week. Ventilation is pretty decent. I did run a dehumidifier and it went away but has come back 

[tvrulesme]

  On 05/12/2024 at 18:21, joe90 said:

I think the wall has previously been “cured” as I said above with waterproof render (but shows it’s not!!!,) it’s a shame it’s all decorated as any work will cause mess. Unless you want to hack plaster off you won’t know. I would look into either an Injected damp course or cut a physical one in. It would mean removing the skirting board but save lots of messy other work 

Expand  

So you think it's coming from the floor, not the exterior? And then bypassing the botched damp proofing?

[joe90]

  On 05/12/2024 at 18:31, tvrulesme said:

So you think it's coming from the floor, not the exterior? And then bypassing the botched damp proofing?

Expand  

That would be my guess, damp rising above the previous “cure”. Houses should have a damp proof course because below ground is damp. I can’t see why a horizontal damp line on an internal wall could be caused by damp on an adjoining wall. Let’s see if others here have another theory.

[Pocster]

Quite possibly damp . I have a rental where tenant pays the utilities and they hardly ever put the heating on . Internal wall with ‘damp’ showing . Previously I paid the bills and so heating would be on - never an issue then …

90degrees to an external wall , damp in middle of wall also …

[Mr Punter]

  On 05/12/2024 at 18:41, Pocster said:

I have a rental where tenant pays the utilities and they hardly ever put the heating on . Internal wall with ‘damp’ showing .

Expand  

 

From tales of your previous tenants it could be wee...

[Roger440]

Id say Joe90 is bang on the money.

[tvrulesme]

  On 05/12/2024 at 18:38, joe90 said:

That would be my guess, damp rising above the previous “cure”. Houses should have a damp proof course because below ground is damp. I can’t see why a horizontal damp line on an internal wall could be caused by damp on an adjoining wall. Let’s see if others here have another theory.

Expand  

 One thing I didn't mention is that a parquet floor is slightly buckled which would indicate damp in the floor. The dryness below is what threw me off course. Thanks @joe90 that makes sense

[tvrulesme]

Just found this after I removed wallpaper. 

 

[joe90]

, I was right , new plaster up to mid height, and not all the way to the door frame (which is why your dotted line was vertical near the frame 🤷‍♂️). I will,put money on waterproof render is under that new plaster. Again if it were me I would inject or physically cut a DPC near floor height behind the skirting. (In a previous renovation I cut a DPC into a whole cottage with a brick hand saw one foot at a time slipping DPC membrane in as I went, took weeks but worked.)

 

OOH I LIKE THE PLASTIC ZIPPY DOOR TO KEEP DUST OUT 👍

Edited December 5, 2024 by joe90

[tvrulesme]

@joe90 please tell me to do one if I'm asking too much. You've been more than enough help already. 

 

I like the idea of the physical DPC given the conflicting views on the effectiveness of chemical. Just so I've understood, you physically cut through the brick behind the skirting to at least the depth of the brick course (~4 inches) approx 1 foot at a time to create a slot, slide in a layer of DPC and continued to the next 1 foot?

 

Just a few questions:

Did you pack the slot with anything? i.e. slate?

Did you have to overlap each 1 foot section of DPC?

 

Mine's not a load bearing wall but just want to minimise settlement cracks 

[joe90]

Only pleased to help mate, I agree with you about injected DPC,.S, I would remove skirting both sides, depending on brick type or mortar used cut  the softest one starting from the door frame, one foot at a time, slide in DPC membrane overlapping as much as possible and pack with slate if you have any or pack with mortar as best as possible, leave enough space to get the saw back in and carry on till you reach the wall. Labour intensive but best solution IMO. You might get a few bricks come loose but you can pack them back in as you go. Don’t try to do all of it in one go, let stuff go off before moving in too far to avoid settlement.

(shame your not close I have loads of slate you could have 🤷‍♂️)

let us know how you get on 👍

[tvrulesme]

  On 06/12/2024 at 08:37, joe90 said:

Only pleased to help mate, I agree with you about injected DPC,.S, I would remove skirting both sides, depending on brick type or mortar used cut  the softest one starting from the door frame, one foot at a time, slide in DPC membrane overlapping as much as possible and pack with slate if you have any or pack with mortar as best as possible, leave enough space to get the saw back in and carry on till you reach the wall. Labour intensive but best solution IMO. You might get a few bricks come loose but you can pack them back in as you go. Don’t try to do all of it in one go, let stuff go off before moving in too far to avoid settlement.

(shame your not close I have loads of slate you could have 🤷‍♂️)

let us know how you get on 👍

Expand  

Brilliant, thanks a lot. Makes perfect sense doing both sides or the moisture will just be pushed to the other side of the wall. I've got a decent 300mm Masonry blade for my reciprocating saw which should make short work of the cuts. 

 

I have tonnes of old slate and reclaimed brick thank you. One of my permanent eBay searches which I act on every time there's a bargain. Will keep this post updated on progress. 

[Temp]

  On 05/12/2024 at 19:37, tvrulesme said:

Just found this after I removed wallpaper. 

 

Expand  

 

Is that the electrical supply for the outside light running along in conduit? 

 

If I zoom in on the outside photo there appears to be vertical lines where the light is? As if the internal wall is there rather than where your red line is?

 

  On 05/12/2024 at 17:18, tvrulesme said:

 

 

 

 

Expand  

 

[tvrulesme]

  On 06/12/2024 at 23:34, Temp said:

Is that the electrical supply for the outside light running along in conduit? 

 

If I zoom in on the outside photo there appears to be vertical lines where the light is? As if the internal wall is there rather than where your red line is?

Expand  

That was an old telephone cable. I was trying to show the outside edge of the internal wall. Wall is directly next to the window

 

\

 

The electricial cable for that lamp ran behind the fascia board. I've removed the lamp and this is the external wall with some of the old paint removed when I was trying to investigate if I had any gaping holes in the wall. Yellow string line is the internal floor level